The United States and Japan will step up their defence cooperation to deal with the threat from nuclear-armed North Korea as tensions in East Asia remain high, officials from the two allies said on Thursday.

Vic rejects jail term link to reoffending

The Victorian government has dismissed a report that found a link between jail time and reoffending, saying it does not adequately distinguish between cause and effect.

Attorney-General Robert Clark criticised the Sentencing Advisory Council report, saying a number of its conclusions were "not backed-up" and while the council generally did good work, "everybody's work is variable".

"It suggests that offenders reoffend because they have been to jail, whereas it is more likely that offenders are sent to jail because they reoffend," a spokesman for Mr Clark said in a statement.

Mr Clark also told ABC Radio in Melbourne it was possible that what was really happening was magistrate's were getting it right.

"When they've got a individual offenders before the court they are more likely to or able to pick those that are more likely to reoffend and are imposing more severe sentences," Mr Clark said.

The report, released on Tuesday, found offenders who have served jail time are "slightly more likely" to reoffend than those sentenced to a non-custodial sentence.

The strongest predictor of reoffending is an offender's recent prior criminal history, the report said.